Process and plant for producing steel

ABSTRACT

A process for producing steel and for obtaining slag having a high content of additional elements such as vanadium in a two-step process. Liquid pig iron is initially blown onto a high-grade slag at a lower temperature, the slag being further processed separately after tapping, while the pig iron is supplied to at least one additional converter in which it is blown at a higher temperature to form steel. A high-grade slag is generated while shortening the steel production process using the process in that the intermediate metal product that is tapped from the first converter is subjected to a heating and/or holding phase before being supplied to the second converter.

The invention is directed to a process and an installation for producing steel and for obtaining slag having a high content of additional elements such as vanadium in a two-step process, wherein the liquid pig iron is initially blown onto a high-grade slag at a lower temperature, the slag being further processed separately after tapping, while the pig iron is supplied to at least one additional converter in which it is blown at a higher temperature to form steel.

The processing times in the first converter in which the high-grade slag is generated are substantially shorter than those for producing the steel in the second converter stage. In order to overcome this disadvantage without having to set aside a waiting time to compensate for the different cycles, two converters are often used in practice in this second processing step.

Another problem which must be considered is that the working temperature in the first step is approximately 1400° C., while the temperature in the steel production step is approximately 1680° C.

Accordingly, whereas waiting times inevitably occur between the first, faster step and the second step in a two-step installation, the installation with two converters in tandem does not make full use of the working capacity of the two converters of the second stage for production of steel.

Apart from this, the total investment costs for two converters in the second stage are naturally higher.

Finally, there are other disadvantages with respect to the process in the installation having only one converter per step because the required waiting time before the second converter can be charged, that is, before this second converter is unoccupied again, leads to loss of production and, in some cases, also considerable problems for the melt because of the inevitable freezing to the transfer vessel.

Therefore, it is the object of the invention to provide a process and an installation which overcome the above-mentioned disadvantages and by which a high-grade slag can be produced on the one hand and the entire steel production process can be shortened on the other hand.

In a process in which the liquid pig iron is initially blown onto a high-grade slag at a lower temperature, the slag being further processed separately after tapping, while the pig iron is supplied to at least one additional converter in which it is blown at a higher temperature to form steel, the above-stated object is met according to the invention in that the intermediate metal product that is tapped from the first converter is subjected to a heating and/or holding phase before being supplied to the second converter.

The heating and/or holding is carried out by metered injection of oxygen.

With respect to the installation, the above-stated object is met according to the invention through the use of a heating stand having an oxygen injection device such as an oxygen lance.

As a result of the process according to the invention, the cycle times between blowing in the first converter and the production of the pig iron in the second converter, which proceeds substantially more slowly, are rendered insignificant because this time period can be bridged in the heating stand.

By supplying oxygen by means of a blowing lance, a portion of the carbon contained in the intermediate metal product is burnt off. The amount of injected oxygen can now be variously metered; specifically, it is possible merely to maintain the temperature during the waiting cycle, that is, to compensate for temperature losses which occur normally.

But, on the other hand, a larger amount of oxygen can also be supplied. In this way, the blowing process in the subsequent converter can be shortened because of the higher carbon burnoff. At the same time, however, the higher burnoff of carbon raises the temperature of the melt so that the higher temperature of about 1680° C. for the second blowing process can be reached already when transferring to the second converter. Also, this substantially reduces the treatment time in this second blowing step.

Because of the resulting overall reduction in treatment time in the installation, productivity can be substantially increased at comparatively lower installation costs compared to an installation with three converters which is limited by the required cycle compensation.

The invention will be described in the following with reference to the drawings.

FIG. 1 is a schematic diagram showing the process flow in an installation according to the invention with a heating stand; and

FIG. 2 is a schematic view of the heating stand;

FIG. 3 shows a two-step installation according to the prior art with three converters;

FIG. 4 shows a corresponding installation with two converters.

FIGS. 3 and 4 show that the liquid pig iron is initially blown in the converter 1 with the aim of achieving a high-grade slag. The temperature is approximately 1400° C. After tapping the slag which is then fed to a refining step, the intermediate metal product is fed after a compulsory waiting period to two converters 2 and 3, where it is blown at approximately 1680° C. to form crude steel which is then subjected to further treatment, for example, in a vacuum installation.

As was already mentioned above, the two converters in tandem in an installation of this kind can often not reach the working capacity of these converters. This disadvantage does not occur in the installation shown in FIG. 4, but in this case the waiting times required for adapting the blowing cycle of the first converter to the second converter constitute a significant, negative factor.

This disadvantage is remedied by the installation according to the invention in which a heating stand is provided between the two converter stages.

FIG. 2 is a schematic view showing how this heating stand might look, namely, by way of the example of an installation having two receptacles for transfer vessels. The left-hand side of the drawing shows the transfer vessel with the intermediate metal product contained therein in the blowing position in which oxygen is supplied or injected through a lance. The right-hand side of the drawing shows a transfer vessel which can be closed by a cover. 

1.-5. (canceled)
 6. A process for producing steel and obtaining slag having a high content of additional elements comprising: blowing liquid pig iron onto a high-grade slag at a first temperature in a first converter; tapping an intermediate metal product from the first converter; subjecting the intermediate metal product to at least one of a heating and a holding phase; tapping the slag from the first converter processing the slag after tapping; and supplying the pig iron intermediate metal product to at least one additional converter in which it is blown at a second temperature to form steel, the second temperature being greater than the first temperature
 7. The process according to claim 6, wherein the intermediate metal product is heated during the holding phase by injecting oxygen.
 8. An apparatus for producing steel and obtaining slag having a high content of additional elements comprising: a transfer vessel configured to transfer an intermediate metal; a first converter for blowing liquid pig iron; at least one second converter for producing crude steel configured to receiving the intermediate metal product tapped from the first converter; and a heating stand configured to station the transfer vessel transferring the intermediate metal product from the first converter to the at least one second converter.
 9. The apparatus according to claim 8, wherein the heating stand is configured to receive a plurality of transfer vessels.
 10. The apparatus according to claim 8, further comprising a device for injecting oxygen into the transfer vessel when the transfer vessel is stationed at the heating stand.
 11. The apparatus according to claim 8, wherein the vessel comprises a cover.
 12. The apparatus according to claim 10, wherein the device for injecting oxygen into the transfer vessel is a lance.
 13. The process according to claim 6, wherein the additional elements comprise vanadium.
 14. The process according to claim 6, wherein the first temperature is about 1400 degrees Celsius.
 15. The process according to claim 6, wherein the second temperature is about 1680 degrees Celsius.
 16. The process according to claim 7, wherein the injected oxygen is metered.
 17. The apparatus according to claim 8, wherein the heating stand is located between the first converter and the at least one second converter. 